In substantially all forms of agriculture, it is common practice to cut the branches, stems and stalks of plants to control or enhance their growth; harvest their products; enhance their appearance; remove or destroy them and the like.
To the above end, the prior art has developed and provides a variety of different kinds of shearing tools specially designed to perform particular cutting operations on different species of plants. Such shearing tools include small one-hand operated shears, larger two-hand operated lopping shears, and pole pruners for reaching and cutting remote branches and the like. The great majority of such shears are single-pass blade and hook type shears characterized by elongate blades and hooks with inner and outer ends, pivot means pivotally connecting the inner ends of the blades and hooks together and manually engageable lever arms projecting from the inner ends of the blade and hooks, opposite from the pivot means.
The hooks of the above type of shears are radially or parabolically curved to define longitudinally extending substantially concaved shearing edges disposed toward their related blades and which serve to receive and retain a branch or the like to be cut. The hooks have flat passing surfaces on radial planes with respect to their pivotal axes and which converge with the referred to shearing edges.
The blades of such shears are flat blades with radially or parabolically curved convex cutting edges disposed towards their related hooks on radial planes immediately adjacent the flat passing surfaces of their related hooks and have flat passing surfaces which oppose and establish sliding engagement with the passing surfaces of the hooks. Such shears are manually pivotally operated from first open positions where the hooks and blades are angularly related to diverge radially relative to each other from their common pivotal axis to closed positions where the cutting and shearing edges of the blades and hooks have moved by each other and the blades and hooks are in substantial parallel juxtaposition. When such shears are moved or actuated from their open to their close positions, branches engaged between the blades and hooks are supported by the hooks and the blades are advanced through and cut them.
In single-pass shears of the class referred to above and here concerned with, the curvature and relationship of the concave shearing edges and convex cutting edges of the shears is carefully designed so that when the blades and hooks are in their open position, the branch engaged therebetween is most effectively retained and is least likely to be urged radially outwardly therebetween or displaced when the shears are advanced from their open to their closed positions. Further, the blades and hooks are designed so that when they are moved from their open to close positions, the raidial inner end portions of the cutting edges lead or are in advance of their related outer portions and the cutting edges effectively slice through and cut the branches cleanly.
In the case of common prior art single-pass blade and hook type shears of the general character referred to, while made to retain and prevent displacement of branches, as above noted, nonetheless tend to displace or eject branches. The tendency for such shears to eject branches increases greatly as the size of branches worked upon increases and as the hardness of the branches increases. For example, large, dry or dead branches of hardwood plants, such as citrus trees and grapevines, are often such that they cannot be easily and satisfactorily cut with shears that will easily and effectively cut green or soft wood branches of equal or greater size. The tendency for such shears to eject large and hard branches is due to the fact that the cutting edges of such shears fail to establish adequate entry into the branches to progressively slice through them. Instead, the cutting edges tend to stop against and slide on or across the branches and thereby urge the branches radially outwardly between the blades and hooks as they are pivoted towards their closed positions.
The prior art has sought to prevent the tendency for shears to eject branches in the manner set forth above by serrating the cutting and/or shearing edges to increase the friction between the branches and those edges and affording greater opportunity for the cutting edges to penetrate the branches. Some in the prior art have claimed that serrating the cutting edges of such shears imparts the shears with a "sawing action", as the cutting edges slice into related branches. This claim has been carefully studied and has been found to have little merit. The most that such serrations appear to do is to first scarify or mutilitate the surfaces of branches worked upon and second, to load up the serrations with vegetable fiber and the like and to thereby reduce the cutting efficiency of the shears.
Other attempts to prevent or reduce the tendency for shears to eject branches in the manner noted above have involved making the cutting edges undulating or sinuate and to thereby seek to capture branches being worked in the valleys of the undulating cutting edges as such shears are closed. The above has proven to be of some benefit in straight-edged hedge shears and the like but the advantages gained are seen to be outweighed by the added cost of establishing such edges and the inconvenience encountered when sharpening such edges. Such sinuate or serpentine edges have proven to be ill-suited for use in other than straight or substantially straight-edged shears.